Whey is the liquid component of milk. During the process of making milk into cheese, whey protein is separated from the curds. Whey is a dilute liquid containing lactose, proteins, salts, and residual fat.
Until recently, a major portion of commercially produced whey was discarded, causing major environmental pollution problems. With the advent of stricter environmental controls and regulations, whey proteins have been reexamined for their utility in the pharmaceutical, dietetic and food industries. Whey proteins have become more heavily incorporated into ice cream, bread, canned soup, infant formulas, and various other food products. Whey is also used as a livestock feed.
Whey proteins possess interesting nutritional, functional, physiological, and pharmaceutical properties. The proteins in whey are divided into two principal groups: 1) the globulin protein fraction containing mainly .beta.-lactoglobulin (.beta.-lg) and immunoglobulins (Ig); and 2) the albumin fraction including .alpha.-lactalbumin (.alpha.-La) and serum albumin. .alpha.-La typically constitutes about 40% by weight of the total proteins in human milk, while cow's milk contains only about 4-5% .alpha.-La by weight of the total proteins.
Whey proteins have been used in infant formula and as a protein source in nutritional mixtures for humans and animals. Since .beta.-lg is not a protein found in human breast-milk, it acts as an allergen to infants. It is therefore desirable for whey proteins in breast-milk substitutes to have either a low concentration of .beta.-lg to reduce the concentration of allergen or a relatively high concentration of .alpha.-La to make it more similar to human milk.
Recent methods of preparing .alpha.-La enriched fractions from milk or whey have included ultrafiltration, heat precipitation, and ion exchange methods. Ultrafiltration methods use membranes which will allow only molecules up to a given size to pass through into the permeate. U.S. Pat. No. 5,008,376 to Bottomley describes a .alpha.-La separation technique using ultrafiltration. Heat precipitation methods involve the application of heat to the whey at a given pH range for a time period sufficient to promote the flocculation of .alpha.-La. Such heat precipitation methods are described in U.S. Pat. No. 5,4 55,331 to Pearce. Ion exchange methods involve contacting the whey with an anion or cation exchanger so as to selectively retain a protein fraction. Such a process is described in U.S. Pat. No. 5,077,067 to Thibault.
The present inventor has now determined that adjusting the pH of the whey to a more acidic level during processing, causes a change in protein conformation and improved retention of the .alpha.-La during later processing. This change in conformation and improved retention provides a high concentration of .alpha.-La in the protein fraction without the need for heat processing or other expensive separation processes.
Accordingly, it is a primary objective of the present invention to provide a method and means of processing whey to obtain a protein fraction having a high concentration of .alpha.-lactalbumin.
It is a further objective of the present invention to provide a method and means of processing whey to obtain a protein fraction having a low concentration of .beta.-lactoglobulin.
It is yet a further objective of the present invention to provide a method and means of processing whey which does not necessitate the application of high temperatures.
It is still a further objective of the present invention to provide a method and means of processing whey to achieve a high concentration of .alpha.-La in the protein fraction which is convenient and economical to use.
The method and means of accomplishing each of the above objectives as well as others will become apparent from the detailed description of the invention which follows hereafter.